1. Field of the invention
The present invention is related to a surface measurement, and more particularly to a method and system for on-line real-time measuring the surface topography and out-of-plane deformation by using phase-shifting shadow moiré method.
2. Description of Related Art
Surface flatness is a common measurement specification over a wide range of manufacturing industries. Flatness critically affects, for example, the reliability and assembly yield of electronic products, the cosmetic appearance and handling characteristics of paper products, and the mechanical fit and functionality of fabricated metal components.
In recent years, lighter and thinner structure of the liquid crystal display (LCD) has become a trend. Correspondingly, the optical components in the back light module (BLM) have become much thinner. Thus, the structural strength of the optical components may be reduced. Light guide plate (LGP) is one of the essential components of a BLM. Warpage may be produced during the manufacturing process due to the lower structural strength of the LGP in a thinner thin film transistor liquid crystal display (TFT-LCD) as required by the market.
This phenomenon has been well known to us for a long time and various methods throughout the past have been proposed and utilized to measure the surface flatness, for example, Scanning Probe Microscopy, Atomic Force Microscopy, Confocal Microscopy, Phase Contrast Microscopy, Differential Interference Contrast Microscopy, etc.
The shadow moiré method is a simple and convenient optical technique for the measurement of surface topography and out-of-plane displacement. For a transparent object such as a LGP, based on the principle of the shadow moiré method, it's required to spray the reflective paint on the object's surface to make the interference fringe pattern sufficiently visible. However, the LGP may no longer be re-used or may be damaged during the process of painting or de-painting.
U.S. Pat. No. 7,369,253 discloses a measurement of sample surface flatness of a continuously moving sample. A conveyor continuously conveys a sample beneath a grating disposed at a non-zero angle with respect to the plane of conveyance. But the patent is used to measure the surface of objects, which comprise a mechanical component, such as a printed circuit board, a sheet material, such as paper, not the transparent materials. In the conventional way, the surfaces of objects are painted a thin layer to reflect the light to the camera for measuring the surface topography of transparent materials.
In view of the foregoing, a need exists in the art for a system and method for measuring surface flatness of continuously moving samples. In addition, a need exists for such a system and method to be efficient and cost-effective.